which is a valid b-tree? group of answer choices root contains keys 12 and 24. the root's left child contains key 18. the root's middle child contains key 11. the root's right child contains key 32. root contains keys 12 and 24. the root's left child contains key 11. the root's middle child contains key 32. the root's right child contains key 18. root contains keys 24 and 12. the root's left child contains key 32. the root's middle child contains key 18. the root's right child contains key 11. root contains keys 12 and 24. the root's left child contains key 9. the root's middle child contains key 18. the root's right child contains key 32.